LINK LEVEL PERFORMANCE EVALUATION OF RELAY-BASED WIMAX NETWORK, Thesis for Telecommunication electronics
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Mustafa__Malik

LINK LEVEL PERFORMANCE EVALUATION OF RELAY-BASED WIMAX NETWORK, Thesis for Telecommunication electronics

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This thesis is focused on analyzing the link-level performance of a relay-based WiMAX network under varying conditions
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i

KWAME NKRUMAH UNIVERSITY OF SCIENCE AND

TECHNOLOGY, KUMASI, GHANA

LINK LEVEL PERFORMANCE EVALUATION OF RELAY-BASED WIMAX

NETWORK

By

THEOPHILUS ANAFO

BEng. (Electronics and Communication Engineering)

A Thesis submitted to the Department of Electrical/Electronic Engineering,

College of Engineering

In partial fulfillment of the requirements for the degree of

MASTER OF SCIENCE

IN

TELECOMMUNICATIONS ENGINEERING

JUNE 2015

ii

Declaration

I hereby declare that, except for specific references which have been duly acknowledged, this

work is the result of my research towards the MSc. Telecommunication Engineering, and

that, to the best of my knowledge, it contains no material previously published by another

person nor material which has been submitted either part or whole for any other degree

elsewhere.

Theophilus Anafo …………………………… …………………………..

(Student) signature Date

Certified by:

Dr. James D. Gadze …....……………………… …………………………..

(Supervisor) signature Date

Certified by:

Mr. Emmanuel A. Frimpong ………………………..… …………………………..

(Head of Department) signature Date

iii

Acknowledgement

My deepest gratitude goes to God Almighty who has sustained me, offering me this

opportunity and granting me the grace to proceed successfully.

I would like to express my profound gratitude to my supervisor Dr. J. D. Gadze for the

enormous continuous support of my Masters Study and research, for his patience, motivation,

enthusiasm, and immense knowledge. His guidance assisted me in every moment of research

and writing of this thesis. I could not have imagined a better supervisor and mentor for my

Masters study. My appreciation goes to the lecturers of the Department of

Electrical/Electronic Engineering, KNUST, for your support and immense knowledge

imparted in me. I'd like to thank my course mates; especially Michael Alewo Oyibo, Sayawu

Yakubu Diaba, Ishmael Amuzu-Quaidoo and Prince Anokye, who rendered encouragements

and many cheerful moments. My sincere thanks go to my pal; Linus Antonio Ofori Agyekum

for his support and many light-hearted moments.

I warmly thank and appreciate my mother; Comfort Anafo, my brothers; Thomas Anafo,

John Anafo and Samuel Anafo for their support and inspiration in all aspects of my life.

I express my gratitude and deepest appreciation to my lovely sweet wife; Joyce Ayinbono

Anafo, and daughter; Cheryl Yensom Anafo, for their great patience and understanding.

iv

Dedication

To my dear wife, Joyce Ayinbono Anafo.

v

Abstract

The recent demand for higher data rate services from wireless network users is

overwhelming. Social media influx as well as the proliferation of smart-phones, tablet

computers and other newly improved wireless devices has erupted a new trend in wireless

network traffic where average capacity and speed is no longer appreciable. In order to cope

with this trend in traffic requirement, wireless network operators are considering a gradual

rollover of an existing third generation (3G) network to a fourth generation (4G) network

with orthogonal frequency division multiple access (OFDMA) based technologies such as

Fourth Generation Long Term Evolution (4G LTE) and Worldwide Interoperability for

Microwave Access (WiMAX). Relay technology promises appreciable network throughput

and coverage enhancement which is required for these systems to function to their optimum

performance. This thesis is focused on analyzing the link-level performance of a relay-based

WiMAX network under varying conditions. The study involves a hypothetical view as well

as MATLAB simulations with results generated which are used to judge the benefit of relay

deployment. This is aimed at solving pertinent issues such as coverage holes and cell edge

problems which are associated with classical non-relay based cellular networks. We

evaluated the performance of relay and direct link communication in terms of BER (Bit Error

Rate), spectral efficiency and capacity. We investigated the effect of multipath fading on link

performance. We also investigated the effect of user speed on performance. Our results

however indicate improved performance in terms of BER, spectral efficiency and capacity in

the downlink when relays are used.

vi

Contents

Declaration ……………………………………………………………………… ii

Acknowledgement ……………………………………………………………… iii

Dedication …………………………………………………………………....... iv

List of Tables ……………………………………………………………………… ix

List of Figures ……………………………………………………………… x

1. Introduction ……………………………………………………………… 1

1.1 Background and Research Motivation ……………………………… 1

1.2 Problem Statement ……………………………………………………… 9

1.3 Motivation ……………………………………………………………… 10

1.4 Research Objective ………………………………………………………. 11

1.4.1 Specific Objectives ……………………………………………… 11

1.5 Thesis Organization ……………………………………………………… 11

2. Literature Review ……………………………………………………… 12

2.1 Introduction ………………………………………………………………. 12

2.2 Wireless cellular network generations ……………………………… 13

2.3 WiMAX Overview ………………………………………………………. 14

2.3.1 The working of WiMAX ……………………………………… 15

2.3.2 Evolutions of WiMAX Standards ……………………………… 16

2.3.3 WiMAX Objectives ……………………………………………… 19

2.3.4 WiMAX Network Architecture ……………………………………… 20

2.3.5 WiMAX OFDM PHY Layer ……………………………………… 23

2.3.5.1 Key Benefits of OFDM ……………………………… 24

vii

2.4 Cellular Relay-based Networks ……………………………………… 27

2.4.1 Characteristics of Relay-based Networks ……………………… 28

2.4.2 Type of Relays ……………………………………………………… 29

2.4.3 Relaying Techniques ……………………………………………… 32

2.4.4 Challenges in Planning Cellular Relay-based Networks ……… 33

2.4.4.1 Relay Placement and Transmission ……………………… 33

2.4.4.2 Path Selection ……………………………………… 35

2.4.4.3 Frequency Re-use ……………………………………… 35

2.4.4.4 Routing Management ……………………………………… 36

2.4.4.5 Resource Allocation ……………………………………… 37

2.4.5 Cooperative Relaying Techniques ……………………………… 39

2.4.6 Performance Evaluation of 802.16j Systems ……………………… 40

2.4.7 Summary ……………………………………………………… 41

3. System Design, Modeling and Simulation ……………………………… 43

3.1. System Model ……………………………………………………... 43

3.2. Channel ……………………………………………………………… 44

3.2.1. Propagation Model ……………………………………………… 45

3.2.1.1. COST-231 Hata Model ……………………………………… 45

3.2.1.2. Stanford University Interim (SUI) Channel Model ……… 46

3.2.2. Multipath Fading Channels ……………………………………… 48

3.3. Relay Strategy ……………………………………………………… 50

3.4. OFDM Implementation in WiMAX ……………………………………… 52

3.5. BER Calculations ……………………………………………………… 55

3.6. Spectral Efficiency ……….……………………………………………… 55

viii

4. System Implementation and Testing ……………………………………... 56

4.1. Introduction ……………………………………………………………… 56

4.2. Simulation Result and Discussion ……………………………………… 56

4.2.1. Performance measure of Relay and Direct links in AWGN channel ... 57

4.2.2. Effect of speed and fading on Performance ……………………… 65

4.2.3. Capacities of relay and direct links ……………………………… 69

5. Conclusion and Recommendations ……………………………………… 71

5.1.Conclusion ……………………………………………………………… 71

Appendix ……………………………………………………………………… 84

A. MATLAB CODES …………………………………………………….. 84

ix

List of Tables

2.1 Generations of mobile cellular networks …………………………………… 13

2.2 Summary of WiMAX standards …………………………………………… 19

x

List of Figures

1.1. Growth charts Mobile-broadband subscription …………………… 1

1.2. Wireless Systems advancement and projections …………………. 2

1.3. Trend of advancement in wireless communication …………………. 3

1.4. WiMAX Network ………………………………………………... 6

1.5. Conventional cellular coverage …………………………………. 7

1.6. Relay WiMAX Network ……………………………………….... 8

2.1. Cellular Network Evolutions ………………………………………. 12

2.2. WiMAX BS Communications …………………………………. 15

2.3. IEEE 802.16 WiMAX Standards …………………………………. 18

2.4. Relay WiMAX Network Reference Model ………………………...… 21

2.5. OFDM signals ……………………………………………………..... 25

2.6. OFDM spectrum efficiency weighed against FDMA spectrum …..... 26

2.7. OFDM subcarrier signals ………………………………………… 26

3.1. System model ……………………………………………………….. 43

3.2. System Implementation with Relay …………………………………. 53

3.3. OFDM symbol structure in frequency domain ………………….. 53

4.1. Plot of BER against Eb/N0 for MS at 60km/h via AWGN channel

(BPSK-1/2) ……………………………………………………… 58

4.2. Spectral Efficiency against Eb/N0 for MS at 60km/h via AWGN

(BPSK-1/2) ...…………………………………………………… 58

4.3. Plot of BER against Eb/N0 for MS at 60km/h via AWGN channel

4.4. (QPSK-1/2) ……………………………………………………… 59

4.5. Spectral Efficiency against Eb/N0 for MS at 60km/h via AWGN

(QPSK-1/2) ...…………………………………………………… 59

xi

4.6. Plot of BER against Eb/N0 for MS at 60km/h via AWGN channel

(QPSK-3/4) ………………………………………………………. 60

4.7. Spectral Efficiency against Eb/N0 for MS at 60km/h via AWGN

(QPSK-3/4) ……………………………………………………… 60

4.8. Plot of BER against Eb/N0 for MS at 60km/h via AWGN channel

(16QAM-1/2) ………………………………………………………. 61

4.9. Spectral Efficiency against Eb/N0 for MS at 60km/h via AWGN

(16-QAM-1/2) ………………………………………………………. 61

4.10. Plot of BER against Eb/N0 for MS at 60km/h via AWGN channel

(16QAM-3/4) ……………………………………………………… 62

4.11. Spectral Efficiency against Eb/N0 for MS at 60km/h via AWGN

(16-QAM-3/4) ……………………………………………………… 62

4.12. Plot of BER against Eb/N0 for MS at 60km/h via AWGN channel

(64QAM-2/3) ……………………………………………………… 63

4.13. Spectral Efficiency against Eb/N0 for MS at 60km/h via AWGN

(64-QAM-2/3) ……………………………………………………… 63

4.14. Plot of BER against Eb/N0 for MS at 60km/h via AWGN channel

(64-QAM-3/4) ……………………………………………………… 64

4.15. Spectral Efficiency against Eb/N0 for MS at 60km/h via AWGN

(64-QAM-3/4) ……………………………………………………… 64

4.16. BER against Eb/N0 for QPSK-1/2 in AWGN, V=30, 60 and

90 km/h …………………………………………………………….. 66

4.17. BER against Eb/N0 for QPSK-1/2 in Fading channel, V=30, 60 and

90 km/h ……………………………………………………………… 66

4.18. BER against Eb/N0 for 16-QAM-1/2 in AWGN, V=30, 60 and

xii

90 km/h ……………………………………………………………... 67

4.19. BER against Eb/N0 for 16-QAM-1/2 in Fading channel, V=30,60 and

90 km/h ……………………………………………………………… 67

4.20. BER against Eb/N0 for 64-QAM-2/3 in AWGN, V=30, 60 and

90 km/h ……………………………………………………………… 68

4.21. BER against Eb/N0 for 64-QAM-1/2 in Fading channel, V=30, 60 and

90 km/h ……………………………………………………………. 68

4.22. Link Capacities of Relay and Direct links against Eb/N0 in pure

AWGN channel …………………………………………………….. 69

4.23. Link Capacities of Relay and Direct links against Eb/N0 in pure

Multipath Fading channel ……………………………………… 70

1

Chapter 1

Introduction

1.1 Background and Research Motivation

Wireless communication has experienced enormous growth in the Telecommunication

industry over the past decades. Presently, there are over six billion eight hundred million

mobile cellular subscribers globally according to the 2014 International Telecommunication

Union (ITU) report. This has mobile-broadband subscriptions approaching two billion three

hundred million in 2014 with 55percent in developing countries. [1][ 2].

Figure 1.1 Growth charts Mobile-broadband subscription

Source: ITU World Telecommunication/ICT Indicator database

This phenomenal trend in growth poses great engineering challenge that only requires

efficient and reliable wireless design.

Third Generation (3G) wireless network systems have been the most widely deployed in

recent years across countries. This has aided entirely new ways of communication,

information access, conducting business and entertainment; while liberating users from slow,

bulky equipment and immobile points of access. The integration of voice, video and data

communication into one network has progressively drifted the demand from wireless voice

services to high speed bandwidth intensive data services [3]. From some point of view, 3G

has been the right bridge for mobile telephony and the internet. Third Generation (3G)

2

wireless network technologies like HSPA and WCDMA have permitted the making of video

calls whiles simultaneously accessing the internet. Also, playing interactive games anywhere

anytime has been made possible with nominal data rates of up to 2.05 Mbps for stationery

devices, 384 Kbps for slowly moving devices and 128 Kbps for fast moving devices [4][ 5].

While the potential of 3G is speedily being transformed into reality, efforts are far advanced

into research with focus on realising systems that can provide even higher data rates and all-

in-one connectivity which is more capable beyond 3G expectation.

The progressive development of mobile communication systems over the years and

projections are depicted in figure 1.2. This clearly indicates that, mobility and data rates are

the main determinants that influence the advancement in wireless systems.

Figure 1.2 Wireless Systems advancement and projections [70]

Before we delve further into the description of the next generation 4G, we first take a snap

view of the progression of radio access depicted in figure 1.3. The technology for the first

generation was analog permitting only voice communication without data access. The second

generation launched in 1995 was based on digital technologies which allowed for data access

but with low transmission rate. This was not enough for multimedia services. Multimedia

3

services were accommodated in the third generation mobile system which was launched

around 2000 [4].

Figure 1.3 Trend of advancement in wireless communication [71]

The recent development of sophisticated mobile devices and the tremendous bandwidth they

require for their efficient use is overwhelming. Furthermore, the increased utilization of

internet based social media and some bandwidth intensive websites such as Youtube, has

ignited the fervent need for even higher speed data networks with higher information bit rates

[3][7]. High throughput is a key requirement particularly in the downlink due to the expected

increase in volumes of data files downloads from servers and websites.

The convergence of Wireless broadband technologies and 3G is expected to meet these

demands of high speed data transmission and has been classified under 4G (Fourth

Generation) systems [5]. 4G networks are expected to offer speed of 100 Mbps in macro-cells

and 1 Gbps in micro-cellular networks. Broadband systems are the regular option expected to

render appreciably high data rates, but it cost network operators so much for the required

spectrum [8]. Consequently, in designing a wireless air interface scheme, spectrum efficiency

is invariably a significant challenge. Complex receivers are normally required in broadband

4

systems to cater for the significant amount of resolvable multipath in a frequency selective

channel [8].

However, 4G seeks to provide optimum connectivity on any device through any network at

anytime and anywhere [6]. Commercial deployment of these systems is in progress and is

replacing 3G technology with features which extend the capabilities of the existing 3G

networks by permitting a wide range of applications with enhanced comprehensive access.

Eventually, 4G networks will incorporate broadband wireless utilities, for example HDTV

(High Definition Television) with speed of 4-20 Mbps and computer network applications

with speed of 1 - 100 Mbps [7]. Such a feature is to appropriate 4G networks to substitute

several utilities of WLAN systems since cost involved for 3G networks to accommodate this

application is significantly high. This is due to the relatively too low spectral efficiency of 3G

networks which is incapable of supporting high data rates at low cost [3]. As a result,

enhanced spectral efficiency is one of the principal emphases of 4G system which has been

significantly improved to offer optimum broadband access.

Additionally to high data rates, 4G systems are required to offer higher QoS (Quality of

Service) of about 98 – 99.5% which is superior to that of 3G cellular systems which aimed to

attain 90 – 95% coverage [5]. This means, the network system is required to be more adaptive

and flexible to be able to attain such level of QoS. For instance, some applications require

network connectivity to be maintained than achieving a high data rate. Therefore, data rate

has to be dropped if transmission path is poor to maintain the link. This might cause data rate

to vary from a very low speed of 1kbps in extremely poor transmission path through to as

high as 20 Mbps when the path is in good condition [7]. Otherwise, additional resources are

allocated to users whose transmission path is poor for applications that require fixed data

rates.

5

The principal summary of 4G is to examine and produce an improved air interface with high

capacity capable of accommodating high mobility, high data rates and high QoS. This is

achieved within a suit of protocols and technologies summarised as follows:

 High peak data rate operation obtained in a wide frequency band with orthogonal

frequency division multiplexing (OFDM).

 Improved spectral efficiency (above 5 bit/s/Hz) with the aid of multiple input multiple

output (MIMO) multiplexing and higher-order modulation.

 Improved data rate at the cell edge via low-rate channel coding, Interference

coordination/cancellation and Transmitter beam-forming/adaptive array antenna

reception.

 Enhanced Multimedia operations with low-delay and highly reliable radio

transmission using error control techniques achieved using hybrid automatic repeat

request (HARQ).

 Flexible radio resource allocation based on the required transmission rate and QoS

with the aid of Orthogonal frequency division multiple access (OFDMA) and

Frequency and time domain scheduling.

 Operation conditions support a maximum terminal speed of 300 km/h with advanced

channel estimation.

There is a great challenge of transmitting high data rate over a wireless link. This is basically

influenced by three limiting factors which are co-channel interference, delay spread and

multipath fading [8]. Multi-carrier technique of transmission has been regarded as ever

promising and suitable for high data rates as well as providing appreciable spectral efficiency

with relatively low implementation cost [5]. Via this scheme of transmission, high rate serial

data stream can be divided into several low rate parallel sub-streams of data modulated on

parallel subcarriers. Consequently, the effect of inter symbol interference (ISI) and delay

6

spread is reduced significantly on the account that the symbol rate on each subcarrier is

considerably less than the initial serial symbol rate [8]. OFDM as a distinctive example of

multicarrier modulation has been vastly employed in the field of digital communication over

a couple of years [28]. However, the challenge of implementation techniques, algorithms and

theory has sustained a persistent interest in the research community. This is manifested in the

degree of amount of publications appearing in conferences and journals over the years.

Presently, there exist a significant number of wireless transmission technologies which are

allotted over different network categories subject to the network scale ranging through PAN,

WLAN, WMAN and WAN. The deployment of wireless networks technology is based on the

demand for higher data transmission rates. Technologies that promise to provide higher data

rates are rapidly enticing more vendors and operators. One of the most capable prospects of

such arising technologies is WiMAX (Worldwide Interoperability for Microwave Access)

described by the IEEE 802.16 standard [9].

WiMAX is intended for wireless metropolitan area networks (WMAN) providing broadband

wireless access up to 50 Km for fixed stations and 5-15 Km for mobile stations [9][10][11].

Figure 1.4 WiMAX Network [72]

Many researchers do believe that WiMAX can propel the wireless data transmission concept

to a greater magnitude than expected. The development of the IEEE 802.16 (WiMAX)

7

standard is as a result of the increasing high capacity and high speed communication demand

for video, voice and multimedia. This impact immensely on the manner people interact or

communicate as well as enjoy their entertainment.

WiMAX standards have evolved through the years since its introduction in 2001 with IEEE

802.16 standard which was also known as fixed WiMAX [19]. The Mobile WiMAX system

came to existence in February 2006. From many industry sources, some important features of

Mobile WiMAX are the utilisation of OFDM, MIMO, AMC, beam-forming and several of

other recent protocols which are categorized as 4G features today. System gain was increased

and portability and mobility enhanced through handovers [10]. The IEEE 802.16j standard

introduced in 2009 sought to enhance coverage, throughput and system capacity by including

mobile multi-hop relay stations (MMR) [11].

A traditional WiMAX cellular network earmarks a BS (base station) to offer services within a

given radius of coverage. The core limitation of this architecture include low spectral

efficiency at cell boundaries as a consequence of low SNR (signal to noise ratio) and

coverage holes as a result of shadowing caused by land forms in mountainous areas and

obstacles such as high rise buildings in urbanized settings. These impede drastically on

transmission resulting in low data rates.

Figure 1.5 Conventional cellular coverage problems

Cellular problems of these nature have received much interests from both academic and

industry researchers with some countermeasures proposed in aspects of interference

8

management such as OFDM, MC-CDMA, etc., and also cooperation techniques such as

MIMO and smart antennas. However, Spectrum efficiency near the cell edge is still poor as

users suffer from enormous path loss and large inter-cell interference. Users require increased

transmit power due to low bit energy to noise rate at these regions in order to maintain bit

fidelity and good throughput. Coverage holes problem also persist in urban and mountainous

areas which deplete coverage to users in shadowed regions [11].

A simple solution to solving these issues is to strategically increase the density of BS within a

geographical area which could also extend coverage to far-reached places. This approach is

however cost ineffective to network operators and inefficient when few users are to be

served. The use of a simple form of a BS called relay is the rapid and cost effective way of

deploying the network infrastructure [16]. Relays do not require E1 or T1 backhaul

connection to communicate with BS that has link connection with some portion of their air

link bandwidth [11]. User information from a nearby mobile station (MS) or user can be

forwarded to a base station with the help of the relay station. Signal coverage can be

effectively extended while enhancing overall throughput via the use of relay. Figure 1.6

shows a typical relay WiMAX network.

Figure 1.6 Relay WiMAX Network [11]

9

Types of relays that can be deployed include NT-RS (non-transparent relay station) and T-RS

(transparent relay station) [17]. NT-RS are usually deployed to offer coverage at cell edge or

beyond coverage of BS. This offer total connectivity interface between the BS and MS where

traffic signal together with control signals and preamble are transmitted through relay. The

other type; T-RS is deployed within BS coverage area to relay only traffic signal between BS

and MS. BS send control information to MS directly in this mode. T-RS are basically used to

improve throughput and capacity within the cell [21].

A well-studied relay technique is the cooperative relay techniques. In cooperative approach,

data is co-operatively transmitted by multiple RSs to MS in downlink or to the BS in uplink

with the aim to enhance system performance [16]. Cooperative technique has enjoyed great

deal of interest from researchers in recent time. It is a suitable scheme for system level

analysis. In this study however, our focus is on link level analysis, quantifying the

performance of a relay link user communicating via a single relay path and examining it

against a direct link user performance. We have based our work on non-cooperative relay

approach, where a single relay path is used to route data from source to destination. Link-

level performance assessment is used in our study to evaluate the activity of a single

communication link while varying link parameters. This result can be used to judge the

possible performance of deploying relays to solve the issues of coverage, throughput and

capacity of a WiMAX cellular system.

1.2 Problem Statement

Several geographical factors, user location and terrestrial obstacles impede connection

between MS and BS hence, making it impossible to achieve the set target of services

anywhere, anytime subscribed in the objectives of IEEE 802.16 WiMAX standard.

10

Traditional architecture of WiMAX cellular system has some resolute drawbacks. These

include coverage holes and degraded spectral efficiency due to low SNR at cell boundaries.

The characteristic usage of relays is to solve this prevalent problem while extending coverage

beyond cell boundaries. However, poor network deployment could cause low performance

and wastage of limited resources.

Link-level performance evaluation is significant to the assessment of the behavior of a single

communication link under varying condition which could provide essential results necessary

to estimate the potential benefit of utilizing relays in solving the issues of coverage holes and

reduced spectral efficiency at cell boundaries.

It is worthwhile therefore, to investigate the performance of relay link usage and compare to

that of the usage of a direct link. A study in this direction will inform the choice and proper

deployment of relays which will enhance coverage and overall cell throughput.

1.3 Motivation

WiMAX is currently one of the most sought after wireless broadband technologies. With the

prevailing demand for higher data rate in wireless communication, WiMAX stand as the

promising landmark technology that could provide the desired solution for high speed

communication. Yet in Ghana, geographical factors and densely packed high rise buildings in

populated urban areas contribute immensely to transmission impairment. Relay technology

promises a cost effective way of solving this issue.

Relay WiMAX described in the IEEE 802.16j standard offer coverage extension beyond cell

borders which is essential in scattered rural settlements. Additionally, OFDM technique has

been adopted as basis for the physical layer of the standard which significantly aids in

achieving the required spectral efficiency for this objective.

11

There are a number of contributions from the research community on different aspects of

multi-hop relay such as frame structure, routing, optimal relay placement, radio resource

management, etc. One aspect which hasn‟t been well studied is link performance; and this has

attracted our interest.

1.4 Research Objective

The main objective of this thesis is to investigate the performances of relay and direct link

users of mobile relay WiMAX under varying link conditions.

1.4.1 Specific Objectives

The specific objectives of this study include:

1. To study and examine the performance of relay link and direct link usage in Additive

White Gaussian Noise (AWGN) by quantifying the bit error rate (BER) and spectral

efficiency against signal to noise ratio (SNR).

2. To investigate the effect of fading channels on performance of relay link and direct

link usage via multipath Rayleigh and Rician channels.

3. To investigate the effect of user speed on performance.

4. To evaluate and compare the capacities of relay and direct links.

1.5 Thesis organization

The thesis is organized as follows: Chapter two presents the literature review. Chapter three

presents the mathematical derivations and system model with parameters necessary for

simulation. In chapter four, link-level simulation is performed to investigate link performance

calculation of BER, spectral efficiency and capacity. Chapter five summarizes the results of

the thesis and informs a potential direction leading to future research.

12

Chapter 2

Literature Review

2.1 Introduction

This chapter presents the literature review; the background and context which form the basis

of the successive chapters. A brief overview of WiMAX and Relay is treated while surveying

some existing literature pertinent to this work and ascertaining possible research axis.

2.2 Wireless cellular network generations

The phenomenal growth in the mobile and wireless communication industry in the past

decade has warranted significant changes to how networks are designed. Voice traffic being

the fundamental focus of the earliest generation of mobile communication framework has

now drifted to emphasize more on high data rate service provision. The first generation (1G)

mobile phone systems, used in the late 1970s through to the late 1980s could carry voice

signal alone between parties in communication [14].

Figure 2.1 Cellular Network Evolutions

In 1991, the second generation (2G) networks which include CDMA, TDMA, GSM, PCS,

and iDEN were commercially launched, presenting digital signaling in telecommunication

13

via packet data transmission while introducing services such as SMS (Short Messaging

Service), MMS (Multimedia Messaging Service) and email [14]. 2.5G, 2.75G and 3G

technologies were subsequently introduced to meet the ever-growing demand on data rate.

With 3G technologies such as WCDMA (Wideband Code Division Multiple Access) and

HSPA (High Speed Packet Access) offering speed of 144Kbps to 2+Mbps, services such as

video on demand, video conferencing, mobile TV, GPS (Global Position System) and

location-based services became attractive and gradually grew into becoming a need than

luxury for a greater number of users. However reaching beyond 3G speed, came the 3.5G

HSDPA (High-Speed Downlink Packet Access) technology, with speed up to 14.4Mbps to

augment 3G performance for web browsing, graphic intensive websites, video conferencing

and on-demand video services [14]. Table 2.1 provides a comprehensive summary of the

advancement of wireless cellular networks.

Table 2.1 Generations of mobile cellular networks [14][15]

Technology 1G 2G 2.5G 3G 4G

Year of

Implementation

1984 1995 1999 2002 2010

Service Analog

voice

Digital

voice,

SMS

Higher

capacity,

packetized

data,

MMS

Higher

capacity,

broadband

data

Higher

capacity,

completely

IP,

multimedia

Standards AMPS,

TACS,

Standards

NMT

TDMA,

CDMA,

GSM, PDC

GPRS, EDGE,

WCDMA,

CDMA2000

Single

standard

Data

Bandwidth

1.9 kbps 14.4 kbps 384 kbps 2 Mbps 200 Mbps

Multiplexing FDMA TDMA,

CDMA

TDMA,

CDMA

CDMA OFDMA,

MC-CDMA

Core Network PSTN PSTN PSTN, packet

network

packet

network

Internet

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